[linux-2.6-omap-h63xx.git] / mm / page_alloc.c

/*
 *  linux/mm/page_alloc.c
 *
 *  Manages the free list, the system allocates free pages here.
 *  Note that kmalloc() lives in slab.c
 *
 *  Copyright (C) 1991, 1992, 1993, 1994  Linus Torvalds
 *  Swap reorganised 29.12.95, Stephen Tweedie
 *  Support of BIGMEM added by Gerhard Wichert, Siemens AG, July 1999
 *  Reshaped it to be a zoned allocator, Ingo Molnar, Red Hat, 1999
 *  Discontiguous memory support, Kanoj Sarcar, SGI, Nov 1999
 *  Zone balancing, Kanoj Sarcar, SGI, Jan 2000
 *  Per cpu hot/cold page lists, bulk allocation, Martin J. Bligh, Sept 2002
 *          (lots of bits borrowed from Ingo Molnar & Andrew Morton)
 */

#include <linux/config.h>
#include <linux/stddef.h>
#include <linux/mm.h>
#include <linux/swap.h>
#include <linux/interrupt.h>
#include <linux/pagemap.h>
#include <linux/bootmem.h>
#include <linux/compiler.h>
#include <linux/kernel.h>
#include <linux/module.h>
#include <linux/suspend.h>
#include <linux/pagevec.h>
#include <linux/blkdev.h>
#include <linux/slab.h>
#include <linux/notifier.h>
#include <linux/topology.h>
#include <linux/sysctl.h>
#include <linux/cpu.h>
#include <linux/cpuset.h>
#include <linux/memory_hotplug.h>
#include <linux/nodemask.h>
#include <linux/vmalloc.h>

#include <asm/tlbflush.h>
#include "internal.h"

/*
 * MCD - HACK: Find somewhere to initialize this EARLY, or make this
 * initializer cleaner
 */
nodemask_t node_online_map __read_mostly = { { [0] = 1UL } };
EXPORT_SYMBOL(node_online_map);
nodemask_t node_possible_map __read_mostly = NODE_MASK_ALL;
EXPORT_SYMBOL(node_possible_map);
struct pglist_data *pgdat_list __read_mostly;
unsigned long totalram_pages __read_mostly;
unsigned long totalhigh_pages __read_mostly;
long nr_swap_pages;

static void fastcall free_hot_cold_page(struct page *page, int cold);

/*
 * results with 256, 32 in the lowmem_reserve sysctl:
 *      1G machine -> (16M dma, 800M-16M normal, 1G-800M high)
 *      1G machine -> (16M dma, 784M normal, 224M high)
 *      NORMAL allocation will leave 784M/256 of ram reserved in the ZONE_DMA
 *      HIGHMEM allocation will leave 224M/32 of ram reserved in ZONE_NORMAL
 *      HIGHMEM allocation will (224M+784M)/256 of ram reserved in ZONE_DMA
 *
 * TBD: should special case ZONE_DMA32 machines here - in those we normally
 * don't need any ZONE_NORMAL reservation
 */
int sysctl_lowmem_reserve_ratio[MAX_NR_ZONES-1] = { 256, 256, 32 };

EXPORT_SYMBOL(totalram_pages);

/*
 * Used by page_zone() to look up the address of the struct zone whose
 * id is encoded in the upper bits of page->flags
 */
struct zone *zone_table[1 << ZONETABLE_SHIFT] __read_mostly;
EXPORT_SYMBOL(zone_table);

static char *zone_names[MAX_NR_ZONES] = { "DMA", "DMA32", "Normal", "HighMem" };
int min_free_kbytes = 1024;

unsigned long __initdata nr_kernel_pages;
unsigned long __initdata nr_all_pages;

#ifdef CONFIG_DEBUG_VM
static int page_outside_zone_boundaries(struct zone *zone, struct page *page)
{
        int ret = 0;
        unsigned seq;
        unsigned long pfn = page_to_pfn(page);

        do {
                seq = zone_span_seqbegin(zone);
                if (pfn >= zone->zone_start_pfn + zone->spanned_pages)
                        ret = 1;
                else if (pfn < zone->zone_start_pfn)
                        ret = 1;
        } while (zone_span_seqretry(zone, seq));

        return ret;
}

static int page_is_consistent(struct zone *zone, struct page *page)
{
#ifdef CONFIG_HOLES_IN_ZONE
        if (!pfn_valid(page_to_pfn(page)))
                return 0;
#endif
        if (zone != page_zone(page))
                return 0;

        return 1;
}
/*
 * Temporary debugging check for pages not lying within a given zone.
 */
static int bad_range(struct zone *zone, struct page *page)
{
        if (page_outside_zone_boundaries(zone, page))
                return 1;
        if (!page_is_consistent(zone, page))
                return 1;

        return 0;
}

#else
static inline int bad_range(struct zone *zone, struct page *page)
{
        return 0;
}
#endif

static void bad_page(struct page *page)
{
        printk(KERN_EMERG "Bad page state in process '%s'\n"
                "page:%p flags:0x%0*lx mapping:%p mapcount:%d count:%d\n"
                "Trying to fix it up, but a reboot is needed\n"
                "Backtrace:\n",
                current->comm, page, (int)(2*sizeof(unsigned long)),
                (unsigned long)page->flags, page->mapping,
                page_mapcount(page), page_count(page));
        dump_stack();
        page->flags &= ~(1 << PG_lru    |
                        1 << PG_private |
                        1 << PG_locked  |
                        1 << PG_active  |
                        1 << PG_dirty   |
                        1 << PG_reclaim |
                        1 << PG_slab    |
                        1 << PG_swapcache |
                        1 << PG_writeback );
        set_page_count(page, 0);
        reset_page_mapcount(page);
        page->mapping = NULL;
        add_taint(TAINT_BAD_PAGE);
}

/*
 * Higher-order pages are called "compound pages".  They are structured thusly:
 *
 * The first PAGE_SIZE page is called the "head page".
 *
 * The remaining PAGE_SIZE pages are called "tail pages".
 *
 * All pages have PG_compound set.  All pages have their ->private pointing at
 * the head page (even the head page has this).
 *
 * The first tail page's ->mapping, if non-zero, holds the address of the
 * compound page's put_page() function.
 *
 * The order of the allocation is stored in the first tail page's ->index
 * This is only for debug at present.  This usage means that zero-order pages
 * may not be compound.
 */
static void prep_compound_page(struct page *page, unsigned long order)
{
        int i;
        int nr_pages = 1 << order;

        page[1].mapping = NULL;
        page[1].index = order;
        for (i = 0; i < nr_pages; i++) {
                struct page *p = page + i;

                SetPageCompound(p);
                set_page_private(p, (unsigned long)page);
        }
}

static void destroy_compound_page(struct page *page, unsigned long order)
{
        int i;
        int nr_pages = 1 << order;

        if (unlikely(page[1].index != order))
                bad_page(page);

        for (i = 0; i < nr_pages; i++) {
                struct page *p = page + i;

                if (unlikely(!PageCompound(p) |
                                (page_private(p) != (unsigned long)page)))
                        bad_page(page);
                ClearPageCompound(p);
        }
}

/*
 * function for dealing with page's order in buddy system.
 * zone->lock is already acquired when we use these.
 * So, we don't need atomic page->flags operations here.
 */
static inline unsigned long page_order(struct page *page) {
        return page_private(page);
}

static inline void set_page_order(struct page *page, int order) {
        set_page_private(page, order);
        __SetPagePrivate(page);
}

static inline void rmv_page_order(struct page *page)
{
        __ClearPagePrivate(page);
        set_page_private(page, 0);
}

/*
 * Locate the struct page for both the matching buddy in our
 * pair (buddy1) and the combined O(n+1) page they form (page).
 *
 * 1) Any buddy B1 will have an order O twin B2 which satisfies
 * the following equation:
 *     B2 = B1 ^ (1 << O)
 * For example, if the starting buddy (buddy2) is #8 its order
 * 1 buddy is #10:
 *     B2 = 8 ^ (1 << 1) = 8 ^ 2 = 10
 *
 * 2) Any buddy B will have an order O+1 parent P which
 * satisfies the following equation:
 *     P = B & ~(1 << O)
 *
 * Assumption: *_mem_map is contigious at least up to MAX_ORDER
 */
static inline struct page *
__page_find_buddy(struct page *page, unsigned long page_idx, unsigned int order)
{
        unsigned long buddy_idx = page_idx ^ (1 << order);

        return page + (buddy_idx - page_idx);
}

static inline unsigned long
__find_combined_index(unsigned long page_idx, unsigned int order)
{
        return (page_idx & ~(1 << order));
}

/*
 * This function checks whether a page is free && is the buddy
 * we can do coalesce a page and its buddy if
 * (a) the buddy is not in a hole &&
 * (b) the buddy is free &&
 * (c) the buddy is on the buddy system &&
 * (d) a page and its buddy have the same order.
 * for recording page's order, we use page_private(page) and PG_private.
 *
 */
static inline int page_is_buddy(struct page *page, int order)
{
#ifdef CONFIG_HOLES_IN_ZONE
        if (!pfn_valid(page_to_pfn(page)))
                return 0;
#endif

       if (PagePrivate(page)           &&
           (page_order(page) == order) &&
            page_count(page) == 0)
               return 1;
       return 0;
}

/*
 * Freeing function for a buddy system allocator.
 *
 * The concept of a buddy system is to maintain direct-mapped table
 * (containing bit values) for memory blocks of various "orders".
 * The bottom level table contains the map for the smallest allocatable
 * units of memory (here, pages), and each level above it describes
 * pairs of units from the levels below, hence, "buddies".
 * At a high level, all that happens here is marking the table entry
 * at the bottom level available, and propagating the changes upward
 * as necessary, plus some accounting needed to play nicely with other
 * parts of the VM system.
 * At each level, we keep a list of pages, which are heads of continuous
 * free pages of length of (1 << order) and marked with PG_Private.Page's
 * order is recorded in page_private(page) field.
 * So when we are allocating or freeing one, we can derive the state of the
 * other.  That is, if we allocate a small block, and both were   
 * free, the remainder of the region must be split into blocks.   
 * If a block is freed, and its buddy is also free, then this
 * triggers coalescing into a block of larger size.            
 *
 * -- wli
 */

static inline void __free_pages_bulk (struct page *page,
                struct zone *zone, unsigned int order)
{
        unsigned long page_idx;
        int order_size = 1 << order;

        if (unlikely(PageCompound(page)))
                destroy_compound_page(page, order);

        page_idx = page_to_pfn(page) & ((1 << MAX_ORDER) - 1);

        BUG_ON(page_idx & (order_size - 1));
        BUG_ON(bad_range(zone, page));

        zone->free_pages += order_size;
        while (order < MAX_ORDER-1) {
                unsigned long combined_idx;
                struct free_area *area;
                struct page *buddy;

                buddy = __page_find_buddy(page, page_idx, order);
                if (!page_is_buddy(buddy, order))
                        break;          /* Move the buddy up one level. */

                list_del(&buddy->lru);
                area = zone->free_area + order;
                area->nr_free--;
                rmv_page_order(buddy);
                combined_idx = __find_combined_index(page_idx, order);
                page = page + (combined_idx - page_idx);
                page_idx = combined_idx;
                order++;
        }
        set_page_order(page, order);
        list_add(&page->lru, &zone->free_area[order].free_list);
        zone->free_area[order].nr_free++;
}

static inline int free_pages_check(struct page *page)
{
        if (unlikely(page_mapcount(page) |
                (page->mapping != NULL)  |
                (page_count(page) != 0)  |
                (page->flags & (
                        1 << PG_lru     |
                        1 << PG_private |
                        1 << PG_locked  |
                        1 << PG_active  |
                        1 << PG_reclaim |
                        1 << PG_slab    |
                        1 << PG_swapcache |
                        1 << PG_writeback |
                        1 << PG_reserved ))))
                bad_page(page);
        if (PageDirty(page))
                __ClearPageDirty(page);
        /*
         * For now, we report if PG_reserved was found set, but do not
         * clear it, and do not free the page.  But we shall soon need
         * to do more, for when the ZERO_PAGE count wraps negative.
         */
        return PageReserved(page);
}

/*
 * Frees a list of pages. 
 * Assumes all pages on list are in same zone, and of same order.
 * count is the number of pages to free.
 *
 * If the zone was previously in an "all pages pinned" state then look to
 * see if this freeing clears that state.
 *
 * And clear the zone's pages_scanned counter, to hold off the "all pages are
 * pinned" detection logic.
 */
static int
free_pages_bulk(struct zone *zone, int count,
                struct list_head *list, unsigned int order)
{
        struct page *page = NULL;
        int ret = 0;

        spin_lock(&zone->lock);
        zone->all_unreclaimable = 0;
        zone->pages_scanned = 0;
        while (!list_empty(list) && count--) {
                page = list_entry(list->prev, struct page, lru);
                /* have to delete it as __free_pages_bulk list manipulates */
                list_del(&page->lru);
                __free_pages_bulk(page, zone, order);
                ret++;
        }
        spin_unlock(&zone->lock);
        return ret;
}

void __free_pages_ok(struct page *page, unsigned int order)
{
        unsigned long flags;
        LIST_HEAD(list);
        int i;
        int reserved = 0;

        arch_free_page(page, order);

#ifndef CONFIG_MMU
        if (order > 0)
                for (i = 1 ; i < (1 << order) ; ++i)
                        __put_page(page + i);
#endif

        for (i = 0 ; i < (1 << order) ; ++i)
                reserved += free_pages_check(page + i);
        if (reserved)
                return;

        list_add(&page->lru, &list);
        mod_page_state(pgfree, 1 << order);
        kernel_map_pages(page, 1<<order, 0);
        local_irq_save(flags);
        free_pages_bulk(page_zone(page), 1, &list, order);
        local_irq_restore(flags);
}

/*
 * permit the bootmem allocator to evade page validation on high-order frees
 */
void fastcall __init __free_pages_bootmem(struct page *page, unsigned int order)
{
        if (order == 0) {
                __ClearPageReserved(page);
                set_page_count(page, 0);

                free_hot_cold_page(page, 0);
        } else {
                LIST_HEAD(list);
                int loop;

                for (loop = 0; loop < BITS_PER_LONG; loop++) {
                        struct page *p = &page[loop];

                        if (loop + 16 < BITS_PER_LONG)
                                prefetchw(p + 16);
                        __ClearPageReserved(p);
                        set_page_count(p, 0);
                }

                arch_free_page(page, order);

                mod_page_state(pgfree, 1 << order);

                list_add(&page->lru, &list);
                kernel_map_pages(page, 1 << order, 0);
                free_pages_bulk(page_zone(page), 1, &list, order);
        }
}


/*
 * The order of subdivision here is critical for the IO subsystem.
 * Please do not alter this order without good reasons and regression
 * testing. Specifically, as large blocks of memory are subdivided,
 * the order in which smaller blocks are delivered depends on the order
 * they're subdivided in this function. This is the primary factor
 * influencing the order in which pages are delivered to the IO
 * subsystem according to empirical testing, and this is also justified
 * by considering the behavior of a buddy system containing a single
 * large block of memory acted on by a series of small allocations.
 * This behavior is a critical factor in sglist merging's success.
 *
 * -- wli
 */
static inline void expand(struct zone *zone, struct page *page,
        int low, int high, struct free_area *area)
{
        unsigned long size = 1 << high;

        while (high > low) {
                area--;
                high--;
                size >>= 1;
                BUG_ON(bad_range(zone, &page[size]));
                list_add(&page[size].lru, &area->free_list);
                area->nr_free++;
                set_page_order(&page[size], high);
        }
}

/*
 * This page is about to be returned from the page allocator
 */
static int prep_new_page(struct page *page, int order)
{
        if (unlikely(page_mapcount(page) |
                (page->mapping != NULL)  |
                (page_count(page) != 0)  |
                (page->flags & (
                        1 << PG_lru     |
                        1 << PG_private |
                        1 << PG_locked  |
                        1 << PG_active  |
                        1 << PG_dirty   |
                        1 << PG_reclaim |
                        1 << PG_slab    |
                        1 << PG_swapcache |
                        1 << PG_writeback |
                        1 << PG_reserved ))))
                bad_page(page);

        /*
         * For now, we report if PG_reserved was found set, but do not
         * clear it, and do not allocate the page: as a safety net.
         */
        if (PageReserved(page))
                return 1;

        page->flags &= ~(1 << PG_uptodate | 1 << PG_error |
                        1 << PG_referenced | 1 << PG_arch_1 |
                        1 << PG_checked | 1 << PG_mappedtodisk);
        set_page_private(page, 0);
        set_page_refs(page, order);
        kernel_map_pages(page, 1 << order, 1);
        return 0;
}

/* 
 * Do the hard work of removing an element from the buddy allocator.
 * Call me with the zone->lock already held.
 */
static struct page *__rmqueue(struct zone *zone, unsigned int order)
{
        struct free_area * area;
        unsigned int current_order;
        struct page *page;

        for (current_order = order; current_order < MAX_ORDER; ++current_order) {
                area = zone->free_area + current_order;
                if (list_empty(&area->free_list))
                        continue;

                page = list_entry(area->free_list.next, struct page, lru);
                list_del(&page->lru);
                rmv_page_order(page);
                area->nr_free--;
                zone->free_pages -= 1UL << order;
                expand(zone, page, order, current_order, area);
                return page;
        }

        return NULL;
}

/* 
 * Obtain a specified number of elements from the buddy allocator, all under
 * a single hold of the lock, for efficiency.  Add them to the supplied list.
 * Returns the number of new pages which were placed at *list.
 */
static int rmqueue_bulk(struct zone *zone, unsigned int order, 
                        unsigned long count, struct list_head *list)
{
        int i;
        
        spin_lock(&zone->lock);
        for (i = 0; i < count; ++i) {
                struct page *page = __rmqueue(zone, order);
                if (unlikely(page == NULL))
                        break;
                list_add_tail(&page->lru, list);
        }
        spin_unlock(&zone->lock);
        return i;
}

#ifdef CONFIG_NUMA
/* Called from the slab reaper to drain remote pagesets */
void drain_remote_pages(void)
{
        struct zone *zone;
        int i;
        unsigned long flags;

        local_irq_save(flags);
        for_each_zone(zone) {
                struct per_cpu_pageset *pset;

                /* Do not drain local pagesets */
                if (zone->zone_pgdat->node_id == numa_node_id())
                        continue;

                pset = zone->pageset[smp_processor_id()];
                for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) {
                        struct per_cpu_pages *pcp;

                        pcp = &pset->pcp[i];
                        if (pcp->count)
                                pcp->count -= free_pages_bulk(zone, pcp->count,
                                                &pcp->list, 0);
                }
        }
        local_irq_restore(flags);
}
#endif

#if defined(CONFIG_PM) || defined(CONFIG_HOTPLUG_CPU)
static void __drain_pages(unsigned int cpu)
{
        unsigned long flags;
        struct zone *zone;
        int i;

        for_each_zone(zone) {
                struct per_cpu_pageset *pset;

                pset = zone_pcp(zone, cpu);
                for (i = 0; i < ARRAY_SIZE(pset->pcp); i++) {
                        struct per_cpu_pages *pcp;

                        pcp = &pset->pcp[i];
                        local_irq_save(flags);
                        pcp->count -= free_pages_bulk(zone, pcp->count,
                                                &pcp->list, 0);
                        local_irq_restore(flags);
                }
        }
}
#endif /* CONFIG_PM || CONFIG_HOTPLUG_CPU */

#ifdef CONFIG_PM

void mark_free_pages(struct zone *zone)
{
        unsigned long zone_pfn, flags;
        int order;
        struct list_head *curr;

        if (!zone->spanned_pages)
                return;

        spin_lock_irqsave(&zone->lock, flags);
        for (zone_pfn = 0; zone_pfn < zone->spanned_pages; ++zone_pfn)
                ClearPageNosaveFree(pfn_to_page(zone_pfn + zone->zone_start_pfn));

        for (order = MAX_ORDER - 1; order >= 0; --order)
                list_for_each(curr, &zone->free_area[order].free_list) {
                        unsigned long start_pfn, i;

                        start_pfn = page_to_pfn(list_entry(curr, struct page, lru));

                        for (i=0; i < (1<<order); i++)
                                SetPageNosaveFree(pfn_to_page(start_pfn+i));
        }
        spin_unlock_irqrestore(&zone->lock, flags);
}

/*
 * Spill all of this CPU's per-cpu pages back into the buddy allocator.
 */
void drain_local_pages(void)
{
        unsigned long flags;

        local_irq_save(flags);  
        __drain_pages(smp_processor_id());
        local_irq_restore(flags);       
}
#endif /* CONFIG_PM */

static void zone_statistics(struct zonelist *zonelist, struct zone *z)
{
#ifdef CONFIG_NUMA
        unsigned long flags;
        int cpu;
        pg_data_t *pg = z->zone_pgdat;
        pg_data_t *orig = zonelist->zones[0]->zone_pgdat;
        struct per_cpu_pageset *p;

        local_irq_save(flags);
        cpu = smp_processor_id();
        p = zone_pcp(z,cpu);
        if (pg == orig) {
                p->numa_hit++;
        } else {
                p->numa_miss++;
                zone_pcp(zonelist->zones[0], cpu)->numa_foreign++;
        }
        if (pg == NODE_DATA(numa_node_id()))
                p->local_node++;
        else
                p->other_node++;
        local_irq_restore(flags);
#endif
}

/*
 * Free a 0-order page
 */
static void fastcall free_hot_cold_page(struct page *page, int cold)
{
        struct zone *zone = page_zone(page);
        struct per_cpu_pages *pcp;
        unsigned long flags;

        arch_free_page(page, 0);

        if (PageAnon(page))
                page->mapping = NULL;
        if (free_pages_check(page))
                return;

        inc_page_state(pgfree);
        kernel_map_pages(page, 1, 0);

        pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
        local_irq_save(flags);
        list_add(&page->lru, &pcp->list);
        pcp->count++;
        if (pcp->count >= pcp->high)
                pcp->count -= free_pages_bulk(zone, pcp->batch, &pcp->list, 0);
        local_irq_restore(flags);
        put_cpu();
}

void fastcall free_hot_page(struct page *page)
{
        free_hot_cold_page(page, 0);
}
        
void fastcall free_cold_page(struct page *page)
{
        free_hot_cold_page(page, 1);
}

static inline void prep_zero_page(struct page *page, int order, gfp_t gfp_flags)
{
        int i;

        BUG_ON((gfp_flags & (__GFP_WAIT | __GFP_HIGHMEM)) == __GFP_HIGHMEM);
        for(i = 0; i < (1 << order); i++)
                clear_highpage(page + i);
}

/*
 * Really, prep_compound_page() should be called from __rmqueue_bulk().  But
 * we cheat by calling it from here, in the order > 0 path.  Saves a branch
 * or two.
 */
static struct page *
buffered_rmqueue(struct zone *zone, int order, gfp_t gfp_flags)
{
        unsigned long flags;
        struct page *page;
        int cold = !!(gfp_flags & __GFP_COLD);

again:
        if (order == 0) {
                struct per_cpu_pages *pcp;

                page = NULL;
                pcp = &zone_pcp(zone, get_cpu())->pcp[cold];
                local_irq_save(flags);
                if (!pcp->count)
                        pcp->count += rmqueue_bulk(zone, 0,
                                                pcp->batch, &pcp->list);
                if (likely(pcp->count)) {
                        page = list_entry(pcp->list.next, struct page, lru);
                        list_del(&page->lru);
                        pcp->count--;
                }
                local_irq_restore(flags);
                put_cpu();
        } else {
                spin_lock_irqsave(&zone->lock, flags);
                page = __rmqueue(zone, order);
                spin_unlock_irqrestore(&zone->lock, flags);
        }

        if (page != NULL) {
                BUG_ON(bad_range(zone, page));
                mod_page_state_zone(zone, pgalloc, 1 << order);
                if (prep_new_page(page, order))
                        goto again;

                if (gfp_flags & __GFP_ZERO)
                        prep_zero_page(page, order, gfp_flags);

                if (order && (gfp_flags & __GFP_COMP))
                        prep_compound_page(page, order);
        }
        return page;
}

#define ALLOC_NO_WATERMARKS     0x01 /* don't check watermarks at all */
#define ALLOC_WMARK_MIN         0x02 /* use pages_min watermark */
#define ALLOC_WMARK_LOW         0x04 /* use pages_low watermark */
#define ALLOC_WMARK_HIGH        0x08 /* use pages_high watermark */
#define ALLOC_HARDER            0x10 /* try to alloc harder */
#define ALLOC_HIGH              0x20 /* __GFP_HIGH set */
#define ALLOC_CPUSET            0x40 /* check for correct cpuset */

/*
 * Return 1 if free pages are above 'mark'. This takes into account the order
 * of the allocation.
 */
int zone_watermark_ok(struct zone *z, int order, unsigned long mark,
                      int classzone_idx, int alloc_flags)
{
        /* free_pages my go negative - that's OK */
        long min = mark, free_pages = z->free_pages - (1 << order) + 1;
        int o;

        if (alloc_flags & ALLOC_HIGH)
                min -= min / 2;
        if (alloc_flags & ALLOC_HARDER)
                min -= min / 4;

        if (free_pages <= min + z->lowmem_reserve[classzone_idx])
                return 0;
        for (o = 0; o < order; o++) {
                /* At the next order, this order's pages become unavailable */
                free_pages -= z->free_area[o].nr_free << o;

                /* Require fewer higher order pages to be free */
                min >>= 1;

                if (free_pages <= min)
                        return 0;
        }
        return 1;
}

/*
 * get_page_from_freeliest goes through the zonelist trying to allocate
 * a page.
 */
static struct page *
get_page_from_freelist(gfp_t gfp_mask, unsigned int order,
                struct zonelist *zonelist, int alloc_flags)
{
        struct zone **z = zonelist->zones;
        struct page *page = NULL;
        int classzone_idx = zone_idx(*z);

        /*
         * Go through the zonelist once, looking for a zone with enough free.
         * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
         */
        do {
                if ((alloc_flags & ALLOC_CPUSET) &&
                                !cpuset_zone_allowed(*z, gfp_mask))
                        continue;

                if (!(alloc_flags & ALLOC_NO_WATERMARKS)) {
                        unsigned long mark;
                        if (alloc_flags & ALLOC_WMARK_MIN)
                                mark = (*z)->pages_min;
                        else if (alloc_flags & ALLOC_WMARK_LOW)
                                mark = (*z)->pages_low;
                        else
                                mark = (*z)->pages_high;
                        if (!zone_watermark_ok(*z, order, mark,
                                    classzone_idx, alloc_flags))
                                continue;
                }

                page = buffered_rmqueue(*z, order, gfp_mask);
                if (page) {
                        zone_statistics(zonelist, *z);
                        break;
                }
        } while (*(++z) != NULL);
        return page;
}

/*
 * This is the 'heart' of the zoned buddy allocator.
 */
struct page * fastcall
__alloc_pages(gfp_t gfp_mask, unsigned int order,
                struct zonelist *zonelist)
{
        const gfp_t wait = gfp_mask & __GFP_WAIT;
        struct zone **z;
        struct page *page;
        struct reclaim_state reclaim_state;
        struct task_struct *p = current;
        int do_retry;
        int alloc_flags;
        int did_some_progress;

        might_sleep_if(wait);

restart:
        z = zonelist->zones;  /* the list of zones suitable for gfp_mask */

        if (unlikely(*z == NULL)) {
                /* Should this ever happen?? */
                return NULL;
        }

        page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
                                zonelist, ALLOC_WMARK_LOW|ALLOC_CPUSET);
        if (page)
                goto got_pg;

        do {
                wakeup_kswapd(*z, order);
        } while (*(++z));

        /*
         * OK, we're below the kswapd watermark and have kicked background
         * reclaim. Now things get more complex, so set up alloc_flags according
         * to how we want to proceed.
         *
         * The caller may dip into page reserves a bit more if the caller
         * cannot run direct reclaim, or if the caller has realtime scheduling
         * policy.
         */
        alloc_flags = ALLOC_WMARK_MIN;
        if ((unlikely(rt_task(p)) && !in_interrupt()) || !wait)
                alloc_flags |= ALLOC_HARDER;
        if (gfp_mask & __GFP_HIGH)
                alloc_flags |= ALLOC_HIGH;
        alloc_flags |= ALLOC_CPUSET;

        /*
         * Go through the zonelist again. Let __GFP_HIGH and allocations
         * coming from realtime tasks go deeper into reserves.
         *
         * This is the last chance, in general, before the goto nopage.
         * Ignore cpuset if GFP_ATOMIC (!wait) rather than fail alloc.
         * See also cpuset_zone_allowed() comment in kernel/cpuset.c.
         */
        page = get_page_from_freelist(gfp_mask, order, zonelist, alloc_flags);
        if (page)
                goto got_pg;

        /* This allocation should allow future memory freeing. */

        if (((p->flags & PF_MEMALLOC) || unlikely(test_thread_flag(TIF_MEMDIE)))
                        && !in_interrupt()) {
                if (!(gfp_mask & __GFP_NOMEMALLOC)) {
nofail_alloc:
                        /* go through the zonelist yet again, ignoring mins */
                        page = get_page_from_freelist(gfp_mask, order,
                                zonelist, ALLOC_NO_WATERMARKS);
                        if (page)
                                goto got_pg;
                        if (gfp_mask & __GFP_NOFAIL) {
                                blk_congestion_wait(WRITE, HZ/50);
                                goto nofail_alloc;
                        }
                }
                goto nopage;
        }

        /* Atomic allocations - we can't balance anything */
        if (!wait)
                goto nopage;

rebalance:
        cond_resched();

        /* We now go into synchronous reclaim */
        p->flags |= PF_MEMALLOC;
        reclaim_state.reclaimed_slab = 0;
        p->reclaim_state = &reclaim_state;

        did_some_progress = try_to_free_pages(zonelist->zones, gfp_mask);

        p->reclaim_state = NULL;
        p->flags &= ~PF_MEMALLOC;

        cond_resched();

        if (likely(did_some_progress)) {
                page = get_page_from_freelist(gfp_mask, order,
                                                zonelist, alloc_flags);
                if (page)
                        goto got_pg;
        } else if ((gfp_mask & __GFP_FS) && !(gfp_mask & __GFP_NORETRY)) {
                /*
                 * Go through the zonelist yet one more time, keep
                 * very high watermark here, this is only to catch
                 * a parallel oom killing, we must fail if we're still
                 * under heavy pressure.
                 */
                page = get_page_from_freelist(gfp_mask|__GFP_HARDWALL, order,
                                zonelist, ALLOC_WMARK_HIGH|ALLOC_CPUSET);
                if (page)
                        goto got_pg;

                out_of_memory(gfp_mask, order);
                goto restart;
        }

        /*
         * Don't let big-order allocations loop unless the caller explicitly
         * requests that.  Wait for some write requests to complete then retry.
         *
         * In this implementation, __GFP_REPEAT means __GFP_NOFAIL for order
         * <= 3, but that may not be true in other implementations.
         */
        do_retry = 0;
        if (!(gfp_mask & __GFP_NORETRY)) {
                if ((order <= 3) || (gfp_mask & __GFP_REPEAT))
                        do_retry = 1;
                if (gfp_mask & __GFP_NOFAIL)
                        do_retry = 1;
        }
        if (do_retry) {
                blk_congestion_wait(WRITE, HZ/50);
                goto rebalance;
        }

nopage:
        if (!(gfp_mask & __GFP_NOWARN) && printk_ratelimit()) {
                printk(KERN_WARNING "%s: page allocation failure."
                        " order:%d, mode:0x%x\n",
                        p->comm, order, gfp_mask);
                dump_stack();
                show_mem();
        }
got_pg:
        return page;
}

EXPORT_SYMBOL(__alloc_pages);

/*
 * Common helper functions.
 */
fastcall unsigned long __get_free_pages(gfp_t gfp_mask, unsigned int order)
{
        struct page * page;
        page = alloc_pages(gfp_mask, order);
        if (!page)
                return 0;
        return (unsigned long) page_address(page);
}

EXPORT_SYMBOL(__get_free_pages);

fastcall unsigned long get_zeroed_page(gfp_t gfp_mask)
{
        struct page * page;

        /*
         * get_zeroed_page() returns a 32-bit address, which cannot represent
         * a highmem page
         */
        BUG_ON((gfp_mask & __GFP_HIGHMEM) != 0);

        page = alloc_pages(gfp_mask | __GFP_ZERO, 0);
        if (page)
                return (unsigned long) page_address(page);
        return 0;
}

EXPORT_SYMBOL(get_zeroed_page);

void __pagevec_free(struct pagevec *pvec)
{
        int i = pagevec_count(pvec);

        while (--i >= 0)
                free_hot_cold_page(pvec->pages[i], pvec->cold);
}

fastcall void __free_pages(struct page *page, unsigned int order)
{
        if (put_page_testzero(page)) {
                if (order == 0)
                        free_hot_page(page);
                else
                        __free_pages_ok(page, order);
        }
}

EXPORT_SYMBOL(__free_pages);

fastcall void free_pages(unsigned long addr, unsigned int order)
{
        if (addr != 0) {
                BUG_ON(!virt_addr_valid((void *)addr));
                __free_pages(virt_to_page((void *)addr), order);
        }
}

EXPORT_SYMBOL(free_pages);

/*
 * Total amount of free (allocatable) RAM:
 */
unsigned int nr_free_pages(void)
{
        unsigned int sum = 0;
        struct zone *zone;

        for_each_zone(zone)
                sum += zone->free_pages;

        return sum;
}

EXPORT_SYMBOL(nr_free_pages);

#ifdef CONFIG_NUMA
unsigned int nr_free_pages_pgdat(pg_data_t *pgdat)
{
        unsigned int i, sum = 0;

        for (i = 0; i < MAX_NR_ZONES; i++)
                sum += pgdat->node_zones[i].free_pages;

        return sum;
}
#endif

static unsigned int nr_free_zone_pages(int offset)
{
        /* Just pick one node, since fallback list is circular */
        pg_data_t *pgdat = NODE_DATA(numa_node_id());
        unsigned int sum = 0;

        struct zonelist *zonelist = pgdat->node_zonelists + offset;
        struct zone **zonep = zonelist->zones;
        struct zone *zone;

        for (zone = *zonep++; zone; zone = *zonep++) {
                unsigned long size = zone->present_pages;
                unsigned long high = zone->pages_high;
                if (size > high)
                        sum += size - high;
        }

        return sum;
}

/*
 * Amount of free RAM allocatable within ZONE_DMA and ZONE_NORMAL
 */
unsigned int nr_free_buffer_pages(void)
{
        return nr_free_zone_pages(gfp_zone(GFP_USER));
}

/*
 * Amount of free RAM allocatable within all zones
 */
unsigned int nr_free_pagecache_pages(void)
{
        return nr_free_zone_pages(gfp_zone(GFP_HIGHUSER));
}

#ifdef CONFIG_HIGHMEM
unsigned int nr_free_highpages (void)
{
        pg_data_t *pgdat;
        unsigned int pages = 0;

        for_each_pgdat(pgdat)
                pages += pgdat->node_zones[ZONE_HIGHMEM].free_pages;

        return pages;
}
#endif

#ifdef CONFIG_NUMA
static void show_node(struct zone *zone)
{
        printk("Node %d ", zone->zone_pgdat->node_id);
}
#else
#define show_node(zone) do { } while (0)
#endif

/*
 * Accumulate the page_state information across all CPUs.
 * The result is unavoidably approximate - it can change
 * during and after execution of this function.
 */
static DEFINE_PER_CPU(struct page_state, page_states) = {0};

atomic_t nr_pagecache = ATOMIC_INIT(0);
EXPORT_SYMBOL(nr_pagecache);
#ifdef CONFIG_SMP
DEFINE_PER_CPU(long, nr_pagecache_local) = 0;
#endif

static void __get_page_state(struct page_state *ret, int nr, cpumask_t *cpumask)
{
        int cpu = 0;

        memset(ret, 0, sizeof(*ret));

        cpu = first_cpu(*cpumask);
        while (cpu < NR_CPUS) {
                unsigned long *in, *out, off;

                in = (unsigned long *)&per_cpu(page_states, cpu);

                cpu = next_cpu(cpu, *cpumask);

                if (cpu < NR_CPUS)
                        prefetch(&per_cpu(page_states, cpu));

                out = (unsigned long *)ret;
                for (off = 0; off < nr; off++)
                        *out++ += *in++;
        }
}

void get_page_state_node(struct page_state *ret, int node)
{
        int nr;
        cpumask_t mask = node_to_cpumask(node);

        nr = offsetof(struct page_state, GET_PAGE_STATE_LAST);
        nr /= sizeof(unsigned long);

        __get_page_state(ret, nr+1, &mask);
}

void get_page_state(struct page_state *ret)
{
        int nr;
        cpumask_t mask = CPU_MASK_ALL;

        nr = offsetof(struct page_state, GET_PAGE_STATE_LAST);
        nr /= sizeof(unsigned long);

        __get_page_state(ret, nr + 1, &mask);
}

void get_full_page_state(struct page_state *ret)
{
        cpumask_t mask = CPU_MASK_ALL;

        __get_page_state(ret, sizeof(*ret) / sizeof(unsigned long), &mask);
}

unsigned long __read_page_state(unsigned long offset)
{
        unsigned long ret = 0;
        int cpu;

        for_each_cpu(cpu) {
                unsigned long in;

                in = (unsigned long)&per_cpu(page_states, cpu) + offset;
                ret += *((unsigned long *)in);
        }
        return ret;
}

void __mod_page_state(unsigned long offset, unsigned long delta)
{
        unsigned long flags;
        void* ptr;

        local_irq_save(flags);
        ptr = &__get_cpu_var(page_states);
        *(unsigned long*)(ptr + offset) += delta;
        local_irq_restore(flags);
}

EXPORT_SYMBOL(__mod_page_state);

void __get_zone_counts(unsigned long *active, unsigned long *inactive,
                        unsigned long *free, struct pglist_data *pgdat)
{
        struct zone *zones = pgdat->node_zones;
        int i;

        *active = 0;
        *inactive = 0;
        *free = 0;
        for (i = 0; i < MAX_NR_ZONES; i++) {
                *active += zones[i].nr_active;
                *inactive += zones[i].nr_inactive;
                *free += zones[i].free_pages;
        }
}

void get_zone_counts(unsigned long *active,
                unsigned long *inactive, unsigned long *free)
{
        struct pglist_data *pgdat;

        *active = 0;
        *inactive = 0;
        *free = 0;
        for_each_pgdat(pgdat) {
                unsigned long l, m, n;
                __get_zone_counts(&l, &m, &n, pgdat);
                *active += l;
                *inactive += m;
                *free += n;
        }
}

void si_meminfo(struct sysinfo *val)
{
        val->totalram = totalram_pages;
        val->sharedram = 0;
        val->freeram = nr_free_pages();
        val->bufferram = nr_blockdev_pages();
#ifdef CONFIG_HIGHMEM
        val->totalhigh = totalhigh_pages;
        val->freehigh = nr_free_highpages();
#else
        val->totalhigh = 0;
        val->freehigh = 0;
#endif
        val->mem_unit = PAGE_SIZE;
}

EXPORT_SYMBOL(si_meminfo);

#ifdef CONFIG_NUMA
void si_meminfo_node(struct sysinfo *val, int nid)
{
        pg_data_t *pgdat = NODE_DATA(nid);

        val->totalram = pgdat->node_present_pages;
        val->freeram = nr_free_pages_pgdat(pgdat);
        val->totalhigh = pgdat->node_zones[ZONE_HIGHMEM].present_pages;
        val->freehigh = pgdat->node_zones[ZONE_HIGHMEM].free_pages;
        val->mem_unit = PAGE_SIZE;
}
#endif

#define K(x) ((x) << (PAGE_SHIFT-10))

/*
 * Show free area list (used inside shift_scroll-lock stuff)
 * We also calculate the percentage fragmentation. We do this by counting the
 * memory on each free list with the exception of the first item on the list.
 */
void show_free_areas(void)
{
        struct page_state ps;
        int cpu, temperature;
        unsigned long active;
        unsigned long inactive;
        unsigned long free;
        struct zone *zone;

        for_each_zone(zone) {
                show_node(zone);
                printk("%s per-cpu:", zone->name);

                if (!populated_zone(zone)) {
                        printk(" empty\n");
                        continue;
                } else
                        printk("\n");

                for_each_online_cpu(cpu) {
                        struct per_cpu_pageset *pageset;

                        pageset = zone_pcp(zone, cpu);

                        for (temperature = 0; temperature < 2; temperature++)
                                printk("cpu %d %s: high %d, batch %d used:%d\n",
                                        cpu,
                                        temperature ? "cold" : "hot",
                                        pageset->pcp[temperature].high,
                                        pageset->pcp[temperature].batch,
                                        pageset->pcp[temperature].count);
                }
        }

        get_page_state(&ps);
        get_zone_counts(&active, &inactive, &free);

        printk("Free pages: %11ukB (%ukB HighMem)\n",
                K(nr_free_pages()),
                K(nr_free_highpages()));

        printk("Active:%lu inactive:%lu dirty:%lu writeback:%lu "
                "unstable:%lu free:%u slab:%lu mapped:%lu pagetables:%lu\n",
                active,
                inactive,
                ps.nr_dirty,
                ps.nr_writeback,
                ps.nr_unstable,
                nr_free_pages(),
                ps.nr_slab,
                ps.nr_mapped,
                ps.nr_page_table_pages);

        for_each_zone(zone) {
                int i;

                show_node(zone);
                printk("%s"
                        " free:%lukB"
                        " min:%lukB"
                        " low:%lukB"
                        " high:%lukB"
                        " active:%lukB"
                        " inactive:%lukB"
                        " present:%lukB"
                        " pages_scanned:%lu"
                        " all_unreclaimable? %s"
                        "\n",
                        zone->name,
                        K(zone->free_pages),
                        K(zone->pages_min),
                        K(zone->pages_low),
                        K(zone->pages_high),
                        K(zone->nr_active),
                        K(zone->nr_inactive),
                        K(zone->present_pages),
                        zone->pages_scanned,
                        (zone->all_unreclaimable ? "yes" : "no")
                        );
                printk("lowmem_reserve[]:");
                for (i = 0; i < MAX_NR_ZONES; i++)
                        printk(" %lu", zone->lowmem_reserve[i]);
                printk("\n");
        }

        for_each_zone(zone) {
                unsigned long nr, flags, order, total = 0;

                show_node(zone);
                printk("%s: ", zone->name);
                if (!populated_zone(zone)) {
                        printk("empty\n");
                        continue;
                }

                spin_lock_irqsave(&zone->lock, flags);
                for (order = 0; order < MAX_ORDER; order++) {
                        nr = zone->free_area[order].nr_free;
                        total += nr << order;
                        printk("%lu*%lukB ", nr, K(1UL) << order);
                }
                spin_unlock_irqrestore(&zone->lock, flags);
                printk("= %lukB\n", K(total));
        }

        show_swap_cache_info();
}

/*
 * Builds allocation fallback zone lists.
 */
static int __init build_zonelists_node(pg_data_t *pgdat, struct zonelist *zonelist, int j, int k)
{
        switch (k) {
                struct zone *zone;
        default:
                BUG();
        case ZONE_HIGHMEM:
                zone = pgdat->node_zones + ZONE_HIGHMEM;
                if (zone->present_pages) {
#ifndef CONFIG_HIGHMEM
                        BUG();
#endif
                        zonelist->zones[j++] = zone;
                }
        case ZONE_NORMAL:
                zone = pgdat->node_zones + ZONE_NORMAL;
                if (zone->present_pages)
                        zonelist->zones[j++] = zone;
        case ZONE_DMA32:
                zone = pgdat->node_zones + ZONE_DMA32;
                if (zone->present_pages)
                        zonelist->zones[j++] = zone;
        case ZONE_DMA:
                zone = pgdat->node_zones + ZONE_DMA;
                if (zone->present_pages)
                        zonelist->zones[j++] = zone;
        }

        return j;
}

static inline int highest_zone(int zone_bits)
{
        int res = ZONE_NORMAL;
        if (zone_bits & (__force int)__GFP_HIGHMEM)
                res = ZONE_HIGHMEM;
        if (zone_bits & (__force int)__GFP_DMA32)
                res = ZONE_DMA32;
        if (zone_bits & (__force int)__GFP_DMA)
                res = ZONE_DMA;
        return res;
}

#ifdef CONFIG_NUMA
#define MAX_NODE_LOAD (num_online_nodes())
static int __initdata node_load[MAX_NUMNODES];
/**
 * find_next_best_node - find the next node that should appear in a given node's fallback list
 * @node: node whose fallback list we're appending
 * @used_node_mask: nodemask_t of already used nodes
 *
 * We use a number of factors to determine which is the next node that should
 * appear on a given node's fallback list.  The node should not have appeared
 * already in @node's fallback list, and it should be the next closest node
 * according to the distance array (which contains arbitrary distance values
 * from each node to each node in the system), and should also prefer nodes
 * with no CPUs, since presumably they'll have very little allocation pressure
 * on them otherwise.
 * It returns -1 if no node is found.
 */
static int __init find_next_best_node(int node, nodemask_t *used_node_mask)
{
        int i, n, val;
        int min_val = INT_MAX;
        int best_node = -1;

        for_each_online_node(i) {
                cpumask_t tmp;

                /* Start from local node */
                n = (node+i) % num_online_nodes();

                /* Don't want a node to appear more than once */
                if (node_isset(n, *used_node_mask))
                        continue;

                /* Use the local node if we haven't already */
                if (!node_isset(node, *used_node_mask)) {
                        best_node = node;
                        break;
                }

                /* Use the distance array to find the distance */
                val = node_distance(node, n);

                /* Give preference to headless and unused nodes */
                tmp = node_to_cpumask(n);
                if (!cpus_empty(tmp))
                        val += PENALTY_FOR_NODE_WITH_CPUS;

                /* Slight preference for less loaded node */
                val *= (MAX_NODE_LOAD*MAX_NUMNODES);
                val += node_load[n];

                if (val < min_val) {
                        min_val = val;
                        best_node = n;
                }
        }

        if (best_node >= 0)
                node_set(best_node, *used_node_mask);

        return best_node;
}

static void __init build_zonelists(pg_data_t *pgdat)
{
        int i, j, k, node, local_node;
        int prev_node, load;
        struct zonelist *zonelist;
        nodemask_t used_mask;

        /* initialize zonelists */
        for (i = 0; i < GFP_ZONETYPES; i++) {
                zonelist = pgdat->node_zonelists + i;
                zonelist->zones[0] = NULL;
        }

        /* NUMA-aware ordering of nodes */
        local_node = pgdat->node_id;
        load = num_online_nodes();
        prev_node = local_node;
        nodes_clear(used_mask);
        while ((node = find_next_best_node(local_node, &used_mask)) >= 0) {
                /*
                 * We don't want to pressure a particular node.
                 * So adding penalty to the first node in same
                 * distance group to make it round-robin.
                 */
                if (node_distance(local_node, node) !=
                                node_distance(local_node, prev_node))
                        node_load[node] += load;
                prev_node = node;
                load--;
                for (i = 0; i < GFP_ZONETYPES; i++) {
                        zonelist = pgdat->node_zonelists + i;
                        for (j = 0; zonelist->zones[j] != NULL; j++);

                        k = highest_zone(i);

                        j = build_zonelists_node(NODE_DATA(node), zonelist, j, k);
                        zonelist->zones[j] = NULL;
                }
        }
}

#else   /* CONFIG_NUMA */

static void __init build_zonelists(pg_data_t *pgdat)
{
        int i, j, k, node, local_node;

        local_node = pgdat->node_id;
        for (i = 0; i < GFP_ZONETYPES; i++) {
                struct zonelist *zonelist;

                zonelist = pgdat->node_zonelists + i;

                j = 0;
                k = highest_zone(i);
                j = build_zonelists_node(pgdat, zonelist, j, k);
                /*
                 * Now we build the zonelist so that it contains the zones
                 * of all the other nodes.
                 * We don't want to pressure a particular node, so when
                 * building the zones for node N, we make sure that the
                 * zones coming right after the local ones are those from
                 * node N+1 (modulo N)
                 */
                for (node = local_node + 1; node < MAX_NUMNODES; node++) {
                        if (!node_online(node))
                                continue;
                        j = build_zonelists_node(NODE_DATA(node), zonelist, j, k);
                }
                for (node = 0; node < local_node; node++) {
                        if (!node_online(node))
                                continue;
                        j = build_zonelists_node(NODE_DATA(node), zonelist, j, k);
                }

                zonelist->zones[j] = NULL;
        }
}

#endif  /* CONFIG_NUMA */

void __init build_all_zonelists(void)
{
        int i;

        for_each_online_node(i)
                build_zonelists(NODE_DATA(i));
        printk("Built %i zonelists\n", num_online_nodes());
        cpuset_init_current_mems_allowed();
}

/*
 * Helper functions to size the waitqueue hash table.
 * Essentially these want to choose hash table sizes sufficiently
 * large so that collisions trying to wait on pages are rare.
 * But in fact, the number of active page waitqueues on typical
 * systems is ridiculously low, less than 200. So this is even
 * conservative, even though it seems large.
 *
 * The constant PAGES_PER_WAITQUEUE specifies the ratio of pages to
 * waitqueues, i.e. the size of the waitq table given the number of pages.
 */
#define PAGES_PER_WAITQUEUE     256

static inline unsigned long wait_table_size(unsigned long pages)
{
        unsigned long size = 1;

        pages /= PAGES_PER_WAITQUEUE;

        while (size < pages)
                size <<= 1;

        /*
         * Once we have dozens or even hundreds of threads sleeping
         * on IO we've got bigger problems than wait queue collision.
         * Limit the size of the wait table to a reasonable size.
         */
        size = min(size, 4096UL);

        return max(size, 4UL);
}

/*
 * This is an integer logarithm so that shifts can be used later
 * to extract the more random high bits from the multiplicative
 * hash function before the remainder is taken.
 */
static inline unsigned long wait_table_bits(unsigned long size)
{
        return ffz(~size);
}

#define LONG_ALIGN(x) (((x)+(sizeof(long))-1)&~((sizeof(long))-1))

static void __init calculate_zone_totalpages(struct pglist_data *pgdat,
                unsigned long *zones_size, unsigned long *zholes_size)
{
        unsigned long realtotalpages, totalpages = 0;
        int i;

        for (i = 0; i < MAX_NR_ZONES; i++)
                totalpages += zones_size[i];
        pgdat->node_spanned_pages = totalpages;

        realtotalpages = totalpages;
        if (zholes_size)
                for (i = 0; i < MAX_NR_ZONES; i++)
                        realtotalpages -= zholes_size[i];
        pgdat->node_present_pages = realtotalpages;
        printk(KERN_DEBUG "On node %d totalpages: %lu\n", pgdat->node_id, realtotalpages);
}


/*
 * Initially all pages are reserved - free ones are freed
 * up by free_all_bootmem() once the early boot process is
 * done. Non-atomic initialization, single-pass.
 */
void __devinit memmap_init_zone(unsigned long size, int nid, unsigned long zone,
                unsigned long start_pfn)
{
        struct page *page;
        unsigned long end_pfn = start_pfn + size;
        unsigned long pfn;

        for (pfn = start_pfn; pfn < end_pfn; pfn++, page++) {
                if (!early_pfn_valid(pfn))
                        continue;
                page = pfn_to_page(pfn);
                set_page_links(page, zone, nid, pfn);
                set_page_count(page, 1);
                reset_page_mapcount(page);
                SetPageReserved(page);
                INIT_LIST_HEAD(&page->lru);
#ifdef WANT_PAGE_VIRTUAL
                /* The shift won't overflow because ZONE_NORMAL is below 4G. */
                if (!is_highmem_idx(zone))
                        set_page_address(page, __va(pfn << PAGE_SHIFT));
#endif
        }
}

void zone_init_free_lists(struct pglist_data *pgdat, struct zone *zone,
                                unsigned long size)
{
        int order;
        for (order = 0; order < MAX_ORDER ; order++) {
                INIT_LIST_HEAD(&zone->free_area[order].free_list);
                zone->free_area[order].nr_free = 0;
        }
}

#define ZONETABLE_INDEX(x, zone_nr)     ((x << ZONES_SHIFT) | zone_nr)
void zonetable_add(struct zone *zone, int nid, int zid, unsigned long pfn,
                unsigned long size)
{
        unsigned long snum = pfn_to_section_nr(pfn);
        unsigned long end = pfn_to_section_nr(pfn + size);

        if (FLAGS_HAS_NODE)
                zone_table[ZONETABLE_INDEX(nid, zid)] = zone;
        else
                for (; snum <= end; snum++)
                        zone_table[ZONETABLE_INDEX(snum, zid)] = zone;
}

#ifndef __HAVE_ARCH_MEMMAP_INIT
#define memmap_init(size, nid, zone, start_pfn) \
        memmap_init_zone((size), (nid), (zone), (start_pfn))
#endif

static int __devinit zone_batchsize(struct zone *zone)
{
        int batch;

        /*
         * The per-cpu-pages pools are set to around 1000th of the
         * size of the zone.  But no more than 1/2 of a meg.
         *
         * OK, so we don't know how big the cache is.  So guess.
         */
        batch = zone->present_pages / 1024;
        if (batch * PAGE_SIZE > 512 * 1024)
                batch = (512 * 1024) / PAGE_SIZE;
        batch /= 4;             /* We effectively *= 4 below */
        if (batch < 1)
                batch = 1;

        /*
         * Clamp the batch to a 2^n - 1 value. Having a power
         * of 2 value was found to be more likely to have
         * suboptimal cache aliasing properties in some cases.
         *
         * For example if 2 tasks are alternately allocating
         * batches of pages, one task can end up with a lot
         * of pages of one half of the possible page colors
         * and the other with pages of the other colors.
         */
        batch = (1 << (fls(batch + batch/2)-1)) - 1;

        return batch;
}

inline void setup_pageset(struct per_cpu_pageset *p, unsigned long batch)
{
        struct per_cpu_pages *pcp;

        memset(p, 0, sizeof(*p));

        pcp = &p->pcp[0];               /* hot */
        pcp->count = 0;
        pcp->high = 6 * batch;
        pcp->batch = max(1UL, 1 * batch);
        INIT_LIST_HEAD(&pcp->list);

        pcp = &p->pcp[1];               /* cold*/
        pcp->count = 0;
        pcp->high = 2 * batch;
        pcp->batch = max(1UL, batch/2);
        INIT_LIST_HEAD(&pcp->list);
}

#ifdef CONFIG_NUMA
/*
 * Boot pageset table. One per cpu which is going to be used for all
 * zones and all nodes. The parameters will be set in such a way
 * that an item put on a list will immediately be handed over to
 * the buddy list. This is safe since pageset manipulation is done
 * with interrupts disabled.
 *
 * Some NUMA counter updates may also be caught by the boot pagesets.
 *
 * The boot_pagesets must be kept even after bootup is complete for
 * unused processors and/or zones. They do play a role for bootstrapping
 * hotplugged processors.
 *
 * zoneinfo_show() and maybe other functions do
 * not check if the processor is online before following the pageset pointer.
 * Other parts of the kernel may not check if the zone is available.
 */
static struct per_cpu_pageset
        boot_pageset[NR_CPUS];

/*
 * Dynamically allocate memory for the
 * per cpu pageset array in struct zone.
 */
static int __devinit process_zones(int cpu)
{
        struct zone *zone, *dzone;

        for_each_zone(zone) {

                zone->pageset[cpu] = kmalloc_node(sizeof(struct per_cpu_pageset),
                                         GFP_KERNEL, cpu_to_node(cpu));
                if (!zone->pageset[cpu])
                        goto bad;

                setup_pageset(zone->pageset[cpu], zone_batchsize(zone));
        }

        return 0;
bad:
        for_each_zone(dzone) {
                if (dzone == zone)
                        break;
                kfree(dzone->pageset[cpu]);
                dzone->pageset[cpu] = NULL;
        }
        return -ENOMEM;
}

static inline void free_zone_pagesets(int cpu)
{
#ifdef CONFIG_NUMA
        struct zone *zone;

        for_each_zone(zone) {
                struct per_cpu_pageset *pset = zone_pcp(zone, cpu);

                zone_pcp(zone, cpu) = NULL;
                kfree(pset);
        }
#endif
}

static int __devinit pageset_cpuup_callback(struct notifier_block *nfb,
                unsigned long action,
                void *hcpu)
{
        int cpu = (long)hcpu;
        int ret = NOTIFY_OK;

        switch (action) {
                case CPU_UP_PREPARE:
                        if (process_zones(cpu))
                                ret = NOTIFY_BAD;
                        break;
                case CPU_UP_CANCELED:
                case CPU_DEAD:
                        free_zone_pagesets(cpu);
                        break;
                default:
                        break;
        }
        return ret;
}

static struct notifier_block pageset_notifier =
        { &pageset_cpuup_callback, NULL, 0 };

void __init setup_per_cpu_pageset(void)
{
        int err;

        /* Initialize per_cpu_pageset for cpu 0.
         * A cpuup callback will do this for every cpu
         * as it comes online
         */
        err = process_zones(smp_processor_id());
        BUG_ON(err);
        register_cpu_notifier(&pageset_notifier);
}

#endif

static __devinit
void zone_wait_table_init(struct zone *zone, unsigned long zone_size_pages)
{
        int i;
        struct pglist_data *pgdat = zone->zone_pgdat;

        /*
         * The per-page waitqueue mechanism uses hashed waitqueues
         * per zone.
         */
        zone->wait_table_size = wait_table_size(zone_size_pages);
        zone->wait_table_bits = wait_table_bits(zone->wait_table_size);
        zone->wait_table = (wait_queue_head_t *)
                alloc_bootmem_node(pgdat, zone->wait_table_size
                                        * sizeof(wait_queue_head_t));

        for(i = 0; i < zone->wait_table_size; ++i)
                init_waitqueue_head(zone->wait_table + i);
}

static __devinit void zone_pcp_init(struct zone *zone)
{
        int cpu;
        unsigned long batch = zone_batchsize(zone);

        for (cpu = 0; cpu < NR_CPUS; cpu++) {
#ifdef CONFIG_NUMA
                /* Early boot. Slab allocator not functional yet */
                zone->pageset[cpu] = &boot_pageset[cpu];
                setup_pageset(&boot_pageset[cpu],0);
#else
                setup_pageset(zone_pcp(zone,cpu), batch);
#endif
        }
        printk(KERN_DEBUG "  %s zone: %lu pages, LIFO batch:%lu\n",
                zone->name, zone->present_pages, batch);
}

static __devinit void init_currently_empty_zone(struct zone *zone,
                unsigned long zone_start_pfn, unsigned long size)
{
        struct pglist_data *pgdat = zone->zone_pgdat;

        zone_wait_table_init(zone, size);
        pgdat->nr_zones = zone_idx(zone) + 1;

        zone->zone_mem_map = pfn_to_page(zone_start_pfn);
        zone->zone_start_pfn = zone_start_pfn;

        memmap_init(size, pgdat->node_id, zone_idx(zone), zone_start_pfn);

        zone_init_free_lists(pgdat, zone, zone->spanned_pages);
}

/*
 * Set up the zone data structures:
 *   - mark all pages reserved
 *   - mark all memory queues empty
 *   - clear the memory bitmaps
 */
static void __init free_area_init_core(struct pglist_data *pgdat,
                unsigned long *zones_size, unsigned long *zholes_size)
{
        unsigned long j;
        int nid = pgdat->node_id;
        unsigned long zone_start_pfn = pgdat->node_start_pfn;

        pgdat_resize_init(pgdat);
        pgdat->nr_zones = 0;
        init_waitqueue_head(&pgdat->kswapd_wait);
        pgdat->kswapd_max_order = 0;
        
        for (j = 0; j < MAX_NR_ZONES; j++) {
                struct zone *zone = pgdat->node_zones + j;
                unsigned long size, realsize;

                realsize = size = zones_size[j];
                if (zholes_size)
                        realsize -= zholes_size[j];

                if (j < ZONE_HIGHMEM)
                        nr_kernel_pages += realsize;
                nr_all_pages += realsize;

                zone->spanned_pages = size;
                zone->present_pages = realsize;
                zone->name = zone_names[j];
                spin_lock_init(&zone->lock);
                spin_lock_init(&zone->lru_lock);
                zone_seqlock_init(zone);
                zone->zone_pgdat = pgdat;
                zone->free_pages = 0;

                zone->temp_priority = zone->prev_priority = DEF_PRIORITY;

                zone_pcp_init(zone);
                INIT_LIST_HEAD(&zone->active_list);
                INIT_LIST_HEAD(&zone->inactive_list);
                zone->nr_scan_active = 0;
                zone->nr_scan_inactive = 0;
                zone->nr_active = 0;
                zone->nr_inactive = 0;
                atomic_set(&zone->reclaim_in_progress, 0);
                if (!size)
                        continue;

                zonetable_add(zone, nid, j, zone_start_pfn, size);
                init_currently_empty_zone(zone, zone_start_pfn, size);
                zone_start_pfn += size;
        }
}

static void __init alloc_node_mem_map(struct pglist_data *pgdat)
{
        /* Skip empty nodes */
        if (!pgdat->node_spanned_pages)
                return;

#ifdef CONFIG_FLAT_NODE_MEM_MAP
        /* ia64 gets its own node_mem_map, before this, without bootmem */
        if (!pgdat->node_mem_map) {
                unsigned long size;
                struct page *map;

                size = (pgdat->node_spanned_pages + 1) * sizeof(struct page);
                map = alloc_remap(pgdat->node_id, size);
                if (!map)
                        map = alloc_bootmem_node(pgdat, size);
                pgdat->node_mem_map = map;
        }
#ifdef CONFIG_FLATMEM
        /*
         * With no DISCONTIG, the global mem_map is just set as node 0's
         */
        if (pgdat == NODE_DATA(0))
                mem_map = NODE_DATA(0)->node_mem_map;
#endif
#endif /* CONFIG_FLAT_NODE_MEM_MAP */
}

void __init free_area_init_node(int nid, struct pglist_data *pgdat,
                unsigned long *zones_size, unsigned long node_start_pfn,
                unsigned long *zholes_size)
{
        pgdat->node_id = nid;
        pgdat->node_start_pfn = node_start_pfn;
        calculate_zone_totalpages(pgdat, zones_size, zholes_size);

        alloc_node_mem_map(pgdat);

        free_area_init_core(pgdat, zones_size, zholes_size);
}

#ifndef CONFIG_NEED_MULTIPLE_NODES
static bootmem_data_t contig_bootmem_data;
struct pglist_data contig_page_data = { .bdata = &contig_bootmem_data };

EXPORT_SYMBOL(contig_page_data);
#endif

void __init free_area_init(unsigned long *zones_size)
{
        free_area_init_node(0, NODE_DATA(0), zones_size,
                        __pa(PAGE_OFFSET) >> PAGE_SHIFT, NULL);
}

#ifdef CONFIG_PROC_FS

#include <linux/seq_file.h>

static void *frag_start(struct seq_file *m, loff_t *pos)
{
        pg_data_t *pgdat;
        loff_t node = *pos;

        for (pgdat = pgdat_list; pgdat && node; pgdat = pgdat->pgdat_next)
                --node;

        return pgdat;
}

static void *frag_next(struct seq_file *m, void *arg, loff_t *pos)
{
        pg_data_t *pgdat = (pg_data_t *)arg;

        (*pos)++;
        return pgdat->pgdat_next;
}

static void frag_stop(struct seq_file *m, void *arg)
{
}

/* 
 * This walks the free areas for each zone.
 */
static int frag_show(struct seq_file *m, void *arg)
{
        pg_data_t *pgdat = (pg_data_t *)arg;
        struct zone *zone;
        struct zone *node_zones = pgdat->node_zones;
        unsigned long flags;
        int order;

        for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; ++zone) {
                if (!populated_zone(zone))
                        continue;

                spin_lock_irqsave(&zone->lock, flags);
                seq_printf(m, "Node %d, zone %8s ", pgdat->node_id, zone->name);
                for (order = 0; order < MAX_ORDER; ++order)
                        seq_printf(m, "%6lu ", zone->free_area[order].nr_free);
                spin_unlock_irqrestore(&zone->lock, flags);
                seq_putc(m, '\n');
        }
        return 0;
}

struct seq_operations fragmentation_op = {
        .start  = frag_start,
        .next   = frag_next,
        .stop   = frag_stop,
        .show   = frag_show,
};

/*
 * Output information about zones in @pgdat.
 */
static int zoneinfo_show(struct seq_file *m, void *arg)
{
        pg_data_t *pgdat = arg;
        struct zone *zone;
        struct zone *node_zones = pgdat->node_zones;
        unsigned long flags;

        for (zone = node_zones; zone - node_zones < MAX_NR_ZONES; zone++) {
                int i;

                if (!populated_zone(zone))
                        continue;

                spin_lock_irqsave(&zone->lock, flags);
                seq_printf(m, "Node %d, zone %8s", pgdat->node_id, zone->name);
                seq_printf(m,
                           "\n  pages free     %lu"
                           "\n        min      %lu"
                           "\n        low      %lu"
                           "\n        high     %lu"
                           "\n        active   %lu"
                           "\n        inactive %lu"
                           "\n        scanned  %lu (a: %lu i: %lu)"
                           "\n        spanned  %lu"
                           "\n        present  %lu",
                           zone->free_pages,
                           zone->pages_min,
                           zone->pages_low,
                           zone->pages_high,
                           zone->nr_active,
                           zone->nr_inactive,
                           zone->pages_scanned,
                           zone->nr_scan_active, zone->nr_scan_inactive,
                           zone->spanned_pages,
                           zone->present_pages);
                seq_printf(m,
                           "\n        protection: (%lu",
                           zone->lowmem_reserve[0]);
                for (i = 1; i < ARRAY_SIZE(zone->lowmem_reserve); i++)
                        seq_printf(m, ", %lu", zone->lowmem_reserve[i]);
                seq_printf(m,
                           ")"
                           "\n  pagesets");
                for (i = 0; i < ARRAY_SIZE(zone->pageset); i++) {
                        struct per_cpu_pageset *pageset;
                        int j;

                        pageset = zone_pcp(zone, i);
                        for (j = 0; j < ARRAY_SIZE(pageset->pcp); j++) {
                                if (pageset->pcp[j].count)
                                        break;
                        }
                        if (j == ARRAY_SIZE(pageset->pcp))
                                continue;
                        for (j = 0; j < ARRAY_SIZE(pageset->pcp); j++) {
                                seq_printf(m,
                                           "\n    cpu: %i pcp: %i"
                                           "\n              count: %i"
                                           "\n              high:  %i"
                                           "\n              batch: %i",
                                           i, j,
                                           pageset->pcp[j].count,
                                           pageset->pcp[j].high,
                                           pageset->pcp[j].batch);
                        }
#ifdef CONFIG_NUMA
                        seq_printf(m,
                                   "\n            numa_hit:       %lu"
                                   "\n            numa_miss:      %lu"
                                   "\n            numa_foreign:   %lu"
                                   "\n            interleave_hit: %lu"
                                   "\n            local_node:     %lu"
                                   "\n            other_node:     %lu",
                                   pageset->numa_hit,
                                   pageset->numa_miss,
                                   pageset->numa_foreign,
                                   pageset->interleave_hit,
                                   pageset->local_node,
                                   pageset->other_node);
#endif
                }
                seq_printf(m,
                           "\n  all_unreclaimable: %u"
                           "\n  prev_priority:     %i"
                           "\n  temp_priority:     %i"
                           "\n  start_pfn:         %lu",
                           zone->all_unreclaimable,
                           zone->prev_priority,
                           zone->temp_priority,
                           zone->zone_start_pfn);
                spin_unlock_irqrestore(&zone->lock, flags);
                seq_putc(m, '\n');
        }
        return 0;
}

struct seq_operations zoneinfo_op = {
        .start  = frag_start, /* iterate over all zones. The same as in
                               * fragmentation. */
        .next   = frag_next,
        .stop   = frag_stop,
        .show   = zoneinfo_show,
};

static char *vmstat_text[] = {
        "nr_dirty",
        "nr_writeback",
        "nr_unstable",
        "nr_page_table_pages",
        "nr_mapped",
        "nr_slab",

        "pgpgin",
        "pgpgout",
        "pswpin",
        "pswpout",

        "pgalloc_high",
        "pgalloc_normal",
        "pgalloc_dma32",
        "pgalloc_dma",

        "pgfree",
        "pgactivate",
        "pgdeactivate",

        "pgfault",
        "pgmajfault",

        "pgrefill_high",
        "pgrefill_normal",
        "pgrefill_dma32",
        "pgrefill_dma",

        "pgsteal_high",
        "pgsteal_normal",
        "pgsteal_dma32",
        "pgsteal_dma",

        "pgscan_kswapd_high",
        "pgscan_kswapd_normal",
        "pgscan_kswapd_dma32",
        "pgscan_kswapd_dma",

        "pgscan_direct_high",
        "pgscan_direct_normal",
        "pgscan_direct_dma32",
        "pgscan_direct_dma",

        "pginodesteal",
        "slabs_scanned",
        "kswapd_steal",
        "kswapd_inodesteal",
        "pageoutrun",
        "allocstall",

        "pgrotated",
        "nr_bounce",
};

static void *vmstat_start(struct seq_file *m, loff_t *pos)
{
        struct page_state *ps;

        if (*pos >= ARRAY_SIZE(vmstat_text))
                return NULL;

        ps = kmalloc(sizeof(*ps), GFP_KERNEL);
        m->private = ps;
        if (!ps)
                return ERR_PTR(-ENOMEM);
        get_full_page_state(ps);
        ps->pgpgin /= 2;                /* sectors -> kbytes */
        ps->pgpgout /= 2;
        return (unsigned long *)ps + *pos;
}

static void *vmstat_next(struct seq_file *m, void *arg, loff_t *pos)
{
        (*pos)++;
        if (*pos >= ARRAY_SIZE(vmstat_text))
                return NULL;
        return (unsigned long *)m->private + *pos;
}

static int vmstat_show(struct seq_file *m, void *arg)
{
        unsigned long *l = arg;
        unsigned long off = l - (unsigned long *)m->private;

        seq_printf(m, "%s %lu\n", vmstat_text[off], *l);
        return 0;
}

static void vmstat_stop(struct seq_file *m, void *arg)
{
        kfree(m->private);
        m->private = NULL;
}

struct seq_operations vmstat_op = {
        .start  = vmstat_start,
        .next   = vmstat_next,
        .stop   = vmstat_stop,
        .show   = vmstat_show,
};

#endif /* CONFIG_PROC_FS */

#ifdef CONFIG_HOTPLUG_CPU
static int page_alloc_cpu_notify(struct notifier_block *self,
                                 unsigned long action, void *hcpu)
{
        int cpu = (unsigned long)hcpu;
        long *count;
        unsigned long *src, *dest;

        if (action == CPU_DEAD) {
                int i;

                /* Drain local pagecache count. */
                count = &per_cpu(nr_pagecache_local, cpu);
                atomic_add(*count, &nr_pagecache);
                *count = 0;
                local_irq_disable();
                __drain_pages(cpu);

                /* Add dead cpu's page_states to our own. */
                dest = (unsigned long *)&__get_cpu_var(page_states);
                src = (unsigned long *)&per_cpu(page_states, cpu);

                for (i = 0; i < sizeof(struct page_state)/sizeof(unsigned long);
                                i++) {
                        dest[i] += src[i];
                        src[i] = 0;
                }

                local_irq_enable();
        }
        return NOTIFY_OK;
}
#endif /* CONFIG_HOTPLUG_CPU */

void __init page_alloc_init(void)
{
        hotcpu_notifier(page_alloc_cpu_notify, 0);
}

/*
 * setup_per_zone_lowmem_reserve - called whenever
 *      sysctl_lower_zone_reserve_ratio changes.  Ensures that each zone
 *      has a correct pages reserved value, so an adequate number of
 *      pages are left in the zone after a successful __alloc_pages().
 */
static void setup_per_zone_lowmem_reserve(void)
{
        struct pglist_data *pgdat;
        int j, idx;

        for_each_pgdat(pgdat) {
                for (j = 0; j < MAX_NR_ZONES; j++) {
                        struct zone *zone = pgdat->node_zones + j;
                        unsigned long present_pages = zone->present_pages;

                        zone->lowmem_reserve[j] = 0;

                        for (idx = j-1; idx >= 0; idx--) {
                                struct zone *lower_zone;

                                if (sysctl_lowmem_reserve_ratio[idx] < 1)
                                        sysctl_lowmem_reserve_ratio[idx] = 1;

                                lower_zone = pgdat->node_zones + idx;
                                lower_zone->lowmem_reserve[j] = present_pages /
                                        sysctl_lowmem_reserve_ratio[idx];
                                present_pages += lower_zone->present_pages;
                        }
                }
        }
}

/*
 * setup_per_zone_pages_min - called when min_free_kbytes changes.  Ensures 
 *      that the pages_{min,low,high} values for each zone are set correctly 
 *      with respect to min_free_kbytes.
 */
void setup_per_zone_pages_min(void)
{
        unsigned long pages_min = min_free_kbytes >> (PAGE_SHIFT - 10);
        unsigned long lowmem_pages = 0;
        struct zone *zone;
        unsigned long flags;

        /* Calculate total number of !ZONE_HIGHMEM pages */
        for_each_zone(zone) {
                if (!is_highmem(zone))
                        lowmem_pages += zone->present_pages;
        }

        for_each_zone(zone) {
                unsigned long tmp;
                spin_lock_irqsave(&zone->lru_lock, flags);
                tmp = (pages_min * zone->present_pages) / lowmem_pages;
                if (is_highmem(zone)) {
                        /*
                         * __GFP_HIGH and PF_MEMALLOC allocations usually don't
                         * need highmem pages, so cap pages_min to a small
                         * value here.
                         *
                         * The (pages_high-pages_low) and (pages_low-pages_min)
                         * deltas controls asynch page reclaim, and so should
                         * not be capped for highmem.
                         */
                        int min_pages;

                        min_pages = zone->present_pages / 1024;
                        if (min_pages < SWAP_CLUSTER_MAX)
                                min_pages = SWAP_CLUSTER_MAX;
                        if (min_pages > 128)
                                min_pages = 128;
                        zone->pages_min = min_pages;
                } else {
                        /*
                         * If it's a lowmem zone, reserve a number of pages
                         * proportionate to the zone's size.
                         */
                        zone->pages_min = tmp;
                }

                zone->pages_low   = zone->pages_min + tmp / 4;
                zone->pages_high  = zone->pages_min + tmp / 2;
                spin_unlock_irqrestore(&zone->lru_lock, flags);
        }
}

/*
 * Initialise min_free_kbytes.
 *
 * For small machines we want it small (128k min).  For large machines
 * we want it large (64MB max).  But it is not linear, because network
 * bandwidth does not increase linearly with machine size.  We use
 *
 *      min_free_kbytes = 4 * sqrt(lowmem_kbytes), for better accuracy:
 *      min_free_kbytes = sqrt(lowmem_kbytes * 16)
 *
 * which yields
 *
 * 16MB:        512k
 * 32MB:        724k
 * 64MB:        1024k
 * 128MB:       1448k
 * 256MB:       2048k
 * 512MB:       2896k
 * 1024MB:      4096k
 * 2048MB:      5792k
 * 4096MB:      8192k
 * 8192MB:      11584k
 * 16384MB:     16384k
 */
static int __init init_per_zone_pages_min(void)
{
        unsigned long lowmem_kbytes;

        lowmem_kbytes = nr_free_buffer_pages() * (PAGE_SIZE >> 10);

        min_free_kbytes = int_sqrt(lowmem_kbytes * 16);
        if (min_free_kbytes < 128)
                min_free_kbytes = 128;
        if (min_free_kbytes > 65536)
                min_free_kbytes = 65536;
        setup_per_zone_pages_min();
        setup_per_zone_lowmem_reserve();
        return 0;
}
module_init(init_per_zone_pages_min)

/*
 * min_free_kbytes_sysctl_handler - just a wrapper around proc_dointvec() so 
 *      that we can call two helper functions whenever min_free_kbytes
 *      changes.
 */
int min_free_kbytes_sysctl_handler(ctl_table *table, int write, 
        struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
{
        proc_dointvec(table, write, file, buffer, length, ppos);
        setup_per_zone_pages_min();
        return 0;
}

/*
 * lowmem_reserve_ratio_sysctl_handler - just a wrapper around
 *      proc_dointvec() so that we can call setup_per_zone_lowmem_reserve()
 *      whenever sysctl_lowmem_reserve_ratio changes.
 *
 * The reserve ratio obviously has absolutely no relation with the
 * pages_min watermarks. The lowmem reserve ratio can only make sense
 * if in function of the boot time zone sizes.
 */
int lowmem_reserve_ratio_sysctl_handler(ctl_table *table, int write,
        struct file *file, void __user *buffer, size_t *length, loff_t *ppos)
{
        proc_dointvec_minmax(table, write, file, buffer, length, ppos);
        setup_per_zone_lowmem_reserve();
        return 0;
}

__initdata int hashdist = HASHDIST_DEFAULT;

#ifdef CONFIG_NUMA
static int __init set_hashdist(char *str)
{
        if (!str)
                return 0;
        hashdist = simple_strtoul(str, &str, 0);
        return 1;
}
__setup("hashdist=", set_hashdist);
#endif

/*
 * allocate a large system hash table from bootmem
 * - it is assumed that the hash table must contain an exact power-of-2
 *   quantity of entries
 * - limit is the number of hash buckets, not the total allocation size
 */
void *__init alloc_large_system_hash(const char *tablename,
                                     unsigned long bucketsize,
                                     unsigned long numentries,
                                     int scale,
                                     int flags,
                                     unsigned int *_hash_shift,
                                     unsigned int *_hash_mask,
                                     unsigned long limit)
{
        unsigned long long max = limit;
        unsigned long log2qty, size;
        void *table = NULL;

        /* allow the kernel cmdline to have a say */
        if (!numentries) {
                /* round applicable memory size up to nearest megabyte */
                numentries = (flags & HASH_HIGHMEM) ? nr_all_pages : nr_kernel_pages;
                numentries += (1UL << (20 - PAGE_SHIFT)) - 1;
                numentries >>= 20 - PAGE_SHIFT;
                numentries <<= 20 - PAGE_SHIFT;

                /* limit to 1 bucket per 2^scale bytes of low memory */
                if (scale > PAGE_SHIFT)
                        numentries >>= (scale - PAGE_SHIFT);
                else
                        numentries <<= (PAGE_SHIFT - scale);
        }
        /* rounded up to nearest power of 2 in size */
        numentries = 1UL << (long_log2(numentries) + 1);

        /* limit allocation size to 1/16 total memory by default */
        if (max == 0) {
                max = ((unsigned long long)nr_all_pages << PAGE_SHIFT) >> 4;
                do_div(max, bucketsize);
        }

        if (numentries > max)
                numentries = max;

        log2qty = long_log2(numentries);

        do {
                size = bucketsize << log2qty;
                if (flags & HASH_EARLY)
                        table = alloc_bootmem(size);
                else if (hashdist)
                        table = __vmalloc(size, GFP_ATOMIC, PAGE_KERNEL);
                else {
                        unsigned long order;
                        for (order = 0; ((1UL << order) << PAGE_SHIFT) < size; order++)
                                ;
                        table = (void*) __get_free_pages(GFP_ATOMIC, order);
                }
        } while (!table && size > PAGE_SIZE && --log2qty);

        if (!table)
                panic("Failed to allocate %s hash table\n", tablename);

        printk("%s hash table entries: %d (order: %d, %lu bytes)\n",
               tablename,
               (1U << log2qty),
               long_log2(size) - PAGE_SHIFT,
               size);

        if (_hash_shift)
                *_hash_shift = log2qty;
        if (_hash_mask)
                *_hash_mask = (1 << log2qty) - 1;

        return table;
}